A wide variety of devices such as Liquid Crystal Displays (LCDs), smart phones, tablet computers etc. can utilize flat glass sheets. One technique for manufacturing these flat glass sheets is the fusion process. In the fusion process, glass sheets are made by using glass manufacturing vessels that contain precious metals, e.g. platinum or platinum alloys which interface with molten glass. The precious metals are generally considered to be inert in relation to most glasses, and thus should not cause any inclusions in the glass sheets. However, this is not necessarily valid.
For example oxidation reactions can occur at the metal/glass leading to the generation of gaseous inclusions in the molten glass and subsequently the glass sheet. One of the more common oxidation reactions that occurs at the metal/glass interface is the conversion of negatively charged oxygen ions to molecular oxygen caused by the thermal breakdown of water and hydroxyl species in the molten glass. This phenomenon occurs because at the elevated temperatures of glass melting and delivery, a low partial pressure of hydrogen exists in the molten glass. Thus, when hydrogen comes in contact with the precious metal vessel containing the molten glass, the hydrogen rapidly permeates out of the glass manufacturing vessel, depleting the metal/glass interface of hydrogen. For example, for every mole of hydrogen that leaves the glass manufacturing vessel, ½ mole of oxygen is left behind at the glass/metal interface. Thus, as hydrogen leaves the glass manufacturing vessel, the oxygen level or partial pressure of oxygen at the metal/glass interface increases, which leads to the generation of blisters or gaseous inclusions in the molten glass. In addition, there are other reactions which involve the catalyzing or oxidation of other species within the molten glass such as halogens (Cl, F, Br) which can lead to the generation of gaseous inclusions within the molten glass and the resulting glass sheet. Further, there are oxidation reactions which can occur due to electrochemical reactions at the metal/glass interface. These electrochemical reactions can be associated with thermal cells, galvanic cells, high AC or DC current applications and/or grounding situations.
Conventional methods used to address the formation of gaseous inclusions includes the use of arsenic as a fining agent within the fusion process or other glass forming process. Arsenic is among the highest temperature fining agents known, and, when added to the molten glass bath, it allows for O2 release from the glass melt at high melting temperatures (e.g., above 1450° C.). This high temperature O2 release, which aids in the removal of bubbles during the melting and fining stages of glass production results in a glass sheet that is essentially free of gaseous inclusions. Furthermore, any residual oxygen bubbles are reabsorbed by the fining agent due to transition from the reduced to oxidized state on cooling. However, from an environmental point of view it is an undesirable to use arsenic as it is a hazardous material. Additional methods include the use of glass coatings as well as DC protection. There is, however, a need in the art to provide an improved method of addressing gaseous inclusions in a glass forming process.